This invention relates to the processing of semiconductor devices and more specifically relates to the formation of trench type superjunction semiconductor devices.
Superjunction semiconductor devices are known in which a plurality of spaced narrow deep trenches are formed in the surface of a silicon substrate. Dielectric filled trenches may also be needed for other semiconductor devices. These trenches are filled with a dielectric medium. The filling process is complicated because the trenches are very narrow and very deep, for example, 3 to 5 microns wide and 40 to 50 microns deep.
A multistep process has been used employing the deposition of a dielectric, such as an oxide, followed by an etch back process. This was needed due to the dielectric layer non-conformity, i.e., the ratio of the dielectric thickness on the horizontal surface of the substrate to the dielectric thickness on a vertical surface is greater than one. As a result, a gap is formed inside the trench, and to fill the gap completely, the top of the dielectric is etched back, removing all dielectric from the horizontal surface, leaving only the dielectric on the vertical trench surface. This process is then repeated until the gap is completely filled.
It would be desirable to form a dielectric filled trench with a less complex and less costly process.
A further problem with the prior art process is that the dielectric material filling the trench has a temperature coefficient of expansion which differs from that of the monocrystalline silicon in which the trench is formed. Thus, a mechanical stress is applied to the silicon as it is heated during processing and in operation.
It would be desirable to eliminate the stress on the silicon due to differential temperature expansion of a filler and a trench.
In accordance with the invention, a dielectric cap is formed over the top of a narrow, deep trench in silicon to seal the interior volume of the trench, leaving a vacuum or a low pressure high dielectric gas, for example, air, sealed within the trench.
Thus, a dielectric such as a low temperature oxide (LTO) or a PECVD oxide is deposited on the surface of a substrate containing one or more trenches to form a xe2x80x9cbridgexe2x80x9d over the top of each trench. The interior of the trench is fully or partly evacuated during this process and the vacuum or residual gas acts as the desired dielectric.